As communications technologies develop, an M2M (Machine to Machine) technology has been widely applied in various fields. In the M2M technology, to reduce costs, precision of a crystal oscillator of a receive end device is limited, and compared with an original signal sent by a transmit end device, a signal received by the receive end device has a relatively large frequency offset. Therefore, the transmit end device and the receive end device need to perform signal synchronization in a case of a relatively large carrier frequency offset. In the communications field at a present stage, there are many signal synchronization methods. Using LTE (Long Term Evolution) as an example, because a ZC (Zadoff-Chu) sequence has good autocorrelation and a stable amplitude, synchronization is performed by using the ZC sequence as a primary synchronization sequence in the LTE.
In an M2M system, to improve spectrum use efficiency, a frequency may be reused in different cells, to implement single-frequency networking. In the LTE, frequency reuse with a reuse factor of 3 is used for a synchronization channel, and different cells are distinguished by using ZC sequences with different root indexes as primary synchronization sequences. Generally, in the LTE, three groups of cells are distinguished by using primary synchronization sequences, the three groups of cells respectively use ZC sequences with root indexes of 29, 24, and 25 as the primary synchronization sequences, and UE determines, according to cross-correlation between the ZC sequences with different root indexes, a group to which a cell belongs.
If a ZC sequence with a good property can be applied to the M2M technology according to the prior art, signal synchronization in single-frequency networking may be implemented in the M2M system. When single-frequency networking is being performed in the prior art, to distinguish different cells, root indexes of ZC sequences of the cells are different from each other. However, in the M2M technology, a signal received by a receive end device has a relatively large frequency offset. The study found that, only a ZC sequence with a root index being +1 or −1 can meet an M2M synchronization requirement in the case of a relatively large frequency offset, but the only two root indexes cannot meet a requirement of distinguishing different cells in the M2M technology. As a result, unlike the prior art, signal synchronization in single-frequency networking cannot be performed by using a ZC sequence in the M2M technology. The ZC sequence with a root index of −1 refers to a conjugate sequence of the ZC sequence with a root index of 1, and this is the same hereinafter.